In the manufacture of integrated circuits, thick metal contacts are put down, such as by electroplating, in certain predetermined areas. This is generally done by photolithographic techniques, whereby a layer of photoresist is applied over the device, the photoresist is exposed to a patterned light source and developed to form openings in the resist layer. The metal contacts are then applied in the opened areas, and the photoresist is then stripped away with a solvent.
When the metal contacts are comparatively thick, on the order of 1 mil (25.4 microns), thick film resists can be advantageously employed. Such resists are commercially available in specified thicknesses of from about 0.6-3 mils (15-76 microns). These thick layers of resist encompass the electroplated metal so that thick metal contacts can be built up having straight walls.
The residual resist films are generally stripped in a commercial stripper solution, followed by a hot benzene sulfonic acid wash. However, this strong acid tends to attack metal layers on the integrated circuit device, thereby destroying the device.
Thus a search was instigated for a solvent system which would completely remove the photoresist, but which would not attack any materials normally found on integrated circuit devices, including materials such as silicon, silicon dioxide, silicon nitride, aluminum, gold, titanium or platinum, or in any other way introduce impurities or dopants into the integrated circuit materials.